The present invention relates to an improved laminated film having at least one lamina of polyvinylidene chloride film adhered to at least one lamina of chlorinated polyethylene, to the method of forming this improved laminated film, and to packages produced therewith.
Polyvinylidene chloride films, commonly known as Saran, are used extensively in the packaging of food products and the like which are susceptible to deterioration by oxygen and other gases. This film is adequately flexible and effectively impermeable to air and oxygen. In addition, polyvinylidene chloride films exhibit very unique properties in a so-called "supercooled" or amorphous condition during which these films can be readily formed around a product to be packaged without incurring undesirable folds, pleats or the like. For example, in following standard packaging procedures, this film upon being extruded is immediately cooled by advancing the same through a water bath maintained at a temperature of approximately 60.degree. to 100.degree. F. which brings about an amorphous condition in the film that is maintained until the combination of time and temperature conditions causes crystallization. While the film is maintained in its supercooled state without any substantial crystallization occurring, it can be sealed to itself merely by contact and without the application of heat. Thus the film is capable of forming a hermetic seal without substantial pressure and without the application of heat seal techniques.
Generally speaking, the polyvinylidene chloride film in its final crystallized form following the general procedure set forth above exhibits substantially random crystal distribution throughout providing that no substantial stretching of the film occurs during package formation. In this regard, however, it has been found that substantial stretching of the supercooled film tends to induce crystallization thereof even though the film is maintained at supercooled temperatures, the crystallization tending toward patterns of crystal orientation and resulting in a reducing or elimination of the self-sealing or fusing property.
The use of polyvinylidene chloride films in combination with other films, such as, for example, polyvinyl chloride, is well known as is shown in U.S. Pat. Nos. 3,083,106, 3,131,069 and 3,228,168. In this regard, however, it has been found that in using such laminated constructions, it is preferred that a plasticizer or pressure sensitive adhesive be used to obtain the desired hermetic seal between the respective laminated films of a package. For example, in U.S. Pat. No. 3,228,168, the use of a pressure sensitive adhesive in a package formed of a supercooled polyvinylidene chloride film to obtain a peelable and reclosable seal is described.
In accordance with an important aspect of the present invention, it has been found that a peelable seal can be obtained with a polyvinylidene chloride-chlorinated ethylene laminated film in which the chlorine concentration of the chlorinated ethylene lamina is maintained below 60% by weight. Accordingly, an important aspect of the present invention concerns the use of a unique laminated film material for packaging use which film mterial provides a peelable and reclosable seal with rigid polyvinyl chloride, polyvinylidene chloride, nylon, paper, cardboard, polyolefins and like packaging materials.
It has also been found that the novel laminated films of the present invention provide improved low temperature properties which advantageously provide increased flexibility and thereby effectively resist the formation of cracks or openings that not only destroy hermetic conditions but also enable the introduction of bacteria and other contaminants into packages produced therewith. This latter feature is particularly important in food packages which are commonly stored at temperatures of around 0.degree. F. and below at which many conventional laminated films lose most of their flexibility.
It is, therefore, an important object of the present invention to provide an improved laminated film which is particularly suitable for packaging use which laminated film includes at least one lamina of crystallized polyvinylidene chloride which is adhered to a lamina of a non-crystalline or amorphous chlorinated polyethylene film.
Another object of the present invention is to provide a new and improved laminated film material which includes a lamina of flexible polyvinylidene chloride to which at least one lamina of chlorinated polyethylene is firmly bonded.
Another object of the present invention is to provide a new and improved laminated film material which includes a polyvinylidene chloride film and chlorinated polyethylene film which laminated film exhibits unique peelable and reseal characteristics with itself and other packaging materials without the use of a plasticizer adhesive interface or pressure sensitive adhesive.
Another object of the present invention is to provide a new and improved laminated material which exhibits excellent oxygen barrier properties and improved flexibility at low temperatures such as are commonly encountered in the storage of packaged food products.
Another object of the present invention is to provide a method for making a laminated packaging film having at least one lamina of polyvinylidene chloride adhered to a lamina of chlorinated polyethylene which method involves contacting a polyvinylidene chloride film, while in a supercooled state, with a chlorinated polyethylene film so as to effect intimate bonding thereof between the engaging surfaces to provide a laminated film which exhibits the unitary character and general appearance of a single layer film.
Another object of the present invention is to provide a new and improved package having a unique laminated film material which includes at least one lamina of a flexible polyvinylidene chloride film which is adhered to at least one lamina of a chlorinated polyethylene film.
Another object of the present invention is to provide a new and improved package which encloses a product between upper and lower sheets of packaging material, which sheets of packaging material are joined together without any interface of a pressure sensitive adhesive or plasticizer therebetween, wherein the engaging sheets can be readily separated without destruction to either of said sheets to provide access to said product and can be further selectively recombined by merely applying slight pressure thereto to provide a reclosable and hermetic seal for said package.